Electrodeposition of antimony



United States Patent ELECTRODEPOSITION 0F ANTIMONY Arthur H. Du Rose, Euclid, Ohio, assignor to The Harshaw Chemical Company, Elyria, Ohio, a corporation of ()hio No Drawing. Application August 7, 1952, Serial No. 303,160

12 Claims. (Cl. 20445) electroplating but it was found necessary to add large quantities of hydrochloric acid to avoid precipitation. This not only made an undesirable solution to work with from the standpoint of corrosion of equipment and skin injuries but usually explosive or rough crystalline deposits were produced. The use of antimony trifiuoride s also has been described in the prior art and has been preferred over the chloride because it does not tend to produce explosive deposits. This compound, however, is undesirable from the cost standpoint and in an acid solution of pH 2.5 to 4.0 presents corrosion problems and makes the solution somewhat hazardous. Nevertheless, the remarkable solubility of the chlorides and fluorides of antimony and their behavior in the plating solution make it difiicult to assemble a desirable antimony plating solution without using one or both to some extent.

It has now been discovered in accordance with the present invention that the tendency of the antimony chloride to form explosive or rough deposits can be overcome by the use of fluoride ion along with the chloride ion and that the objectionable features of these compounds can be reduced greatly by the use in the solution of an alpha hydroxy carboxylic acid such as tartaric, citric, glycolic, gluconic and lactic acids. 0 The fundamental bath of the present invention is made up of a source of antimony ions of the class consisting of (1) antimony trifluoride and (2) antimony trichloride with antimony trifluoride, an alpha hydroxy carboxylic acid preferably of the class consisting of tartaric, citric, glycolic, gluconic and lactic acids, and means for adjusting the pH of the solution, such as for example ammonium hydroxide or carbonate or the hydroxide or carbonate of an alkali metal, or an amine such as triethanolamine. It is desirable also to have present in the bath means for preventing or insuring against cathode corrosion and immersion deposition, suitably sulfate ion. This is especially important when plating on lead or other metal tending to corrode in the solution or to cause immersion deposition.

When antimony chloride is used with antimony fluoride, the antimony from the chloride may be present up to 40% of the total antimony content.

The quantity of alpha hydroxy carboxylic acid used maybe within the range of A; to 2 hydroxy equivalent weights of the acid per atomic weight of antimony, the preferred concentration being about 1 alpha hydroxy equivalent weight of acid per atomic weight of antimony. (By alpha hydroxy equivalent weight is meant the molecular weightof the alpha hydroxy acid divided by the number of its alpha hydroxy groups.)

The pH of the solution should be within the limits from 2.5 to 5.0.

When sulfate ion is present it should be present in proportion from 50 to 150 mol per cent of the alpha hydroxy acid.

In making up the solutions, the adjustment of the pH may be accomplished or partly so by the choice of compounds. Thus, for example, by using SbzOs and NH4FHF orNH4F, SbFs is produced in situ in the bath or in the tank used for manufacture of concentrate and ammonia is left over for reaction with alpha hydroxy or other acid and thus neutralizes hydrogen ions or forms ammonium hydroxide or both, in either case raising the pH. Additional alkaline material may or may not be needed to secure the desired pH. As a practical matter, it is very desirable to form a bath or a concentrate which requires little if any addition of ammonia to the platers tank. Also, it is cheaper to make use of antimony oxide and an ammonium fluoride instead of using antimony trifluoride as such in making up baths or concentrates. As shown 'by' Examples 11 and 12, Table II, it is feasible to operate without further adjustment of pH after making up the solutions there indicated.

Preferred solutions consist of SbzOs, NHrFHF and glycolic acid in proportions as follows: Sb2O3 from 0.3 to 0.9 mol per liter, NH4FHF from 0.61 to 1.85 mols per liter, glycolic acid from 0.61 to 1.85 mols per liter and NH4OH'to yield a pH from 2.5 to 5.0.

Representative batches for basic' bath formulations in accordance with' the present invention are as shown by way of example in Table I.

TABLE I 7 1 Mols per Liter Preferred Example Range 1 811013 0.87 5 -1. 5 NaF; 2. 61 1. 5 -4. 5 Tartaric Acid 0. 8 25-1. 5 NaOH to p 3.0 2.7 3. 5 2 SbCla j 1.12 .5 1.5 'KF.2HF 1.12 5 -1. 5 Tartaric Acld 1.0 25-1. 5 X013 to pH 3. 5 2. 7 3. 5 3. 1a 1. 25 5 1. 5

NH4F.HF 1. 875 -2. 25 Ammonium citra .31 3 -1. 0 NH40H to pH... 4. 0 2. 5 4. 5 4 SbFa 1.25 .5 1.5 (NHMSOL- l. 25 25-1. 5 Glycolic Acid 0.75 25-1. 5 NH4OH to pH.. 4. 0 2. 5 4. 5 5 SbZOL. 0. 50 25- 75 H01 1. 50 75-2. 0 NH4F.HF 1. 50 75-2. 3 Lactic Acid 25 201. 5 NHiOH to pH 4. 0 2. 5 4. 5 6. D20: 0.62 25- .75 111504.-.- 1. 25 504. 50 KF.HF-. 1. 87 75-2. 25 Glueonlc Ac 75 25-1. 50 KOH 4. 5 7 813203 0. 7 25- 75 HF 4. 2 1. 5 4. 5 Tartaric Acid. .35 .251.5 Triethanolamine to pH 4. 0 3.0 5. 0 8. O3 0.62 25- .75 NH4FHF 1.85 .75-2. 25 Glycolie Aci 1. 23 75-2. 25 4) 280 1. 23 25-2. 25 NH40H to pH 4.0 2. 5 -4. 5 9. bF3 1.23 .5 1.5

SbClg. 31 1 40 Glycolic Acid. 1. 54 6 -1. 9 NHiOH to pH 3. 5 2. 5 1. 5 10. sbzoam- 615 .25- .75 NHiRHF 1. 23 5 1. 50 HF 1. 23 5 -1. 50 Glycolic Ae1d 1. 23 5 1. 50 ms 4 1.23 5 1. 50 NH4OH to pH 4 2. 5 4. 5

The foregoing batch formulae do not show the compositions'of the solutions since some reactions take place. Where these formulations are specified herein, it is to be understood that the reaction or solution product is intended. In Table II are shown, using corresponding numerals, closer approximations to the actual bath compositions. Ionization and complexing are not indicated and some of the indicated reactions do not go all the way to completion. The reactions involved in pH adjustment are also not indicated but are quite obvious.

TABLE II Mols per liter 1. SbF 0.87 NaCl 2.61 Tartaric acid 0.8 NaOH to pH 3.0 2. SbF 1.12

KCl 1.12 HCl 2.24 r Tartaric acid 0.10 KOH to pH 3.5 3. SbFs 1.25

. NH4Cl 1.875

HCl 1.875 9 Ammonium citrate a- 0.31 NHiOI-I to pH 4.0 4. SbFa 1.25 (NH4)2SO4 1.25 Glycolic acid 0.75 r NHiOH to pH 4.0 '5. SbFs 1.00 NH4Cl 1.50 Lactic acid 0.25 NH-lOH to pH 4.0 n 6. SbFs 1.25 K2SO4 .935 H2504 .315 Gluconic acid .75 KOH to pH 4.5 M 7. SbFs 1.4

Tartaric acid .35 Triethanolamine to pH 4.0 8. SbFs 1.25 Ammonium glycolate 1.23 Ammonium sulfate 1.23 40 Ammonium hydroxide to pH 4.0 9. SbFa 1.23 SbCl3 .31 Glycolic acid 1.54 NH4OH to pH 3.5 10. SbFs 1.23 Ammonium glycolate 1.23 Ammonium sulfate 1.23 Ammonium hydroxide to pH 4.0 11. SbFs 1.23

Ammonium glycolate 1.23 12. .SbFs I M 1.23 Ammonium glycolate 1.23 Ammonium sulfate 1.23

Temperature is not sharply critical but may be suitably in the range from 100. to 160 F.

Cathode current density is, likewise, not sharply critical but preferably is in the range from 10 to 200 amperes per square foot.

Addition agents for securing brightness or other improved properties may be added if desired.

The ingredients of the foregoing examples may be sold to the plating trade separately or in the form of a concentrate containing a plurality or all of them and the minimum of water to yield a liquid which can be easily handled in drums, carboys, or the like. It is quite advantageous to market a concentrate which will not attack steel shipping drums and which involves shipment of no water which would not be shipped if the constituents of the bath other than water were shipped separately. In the case of Example 10, for instance, the SbzOs, NHiFHF, HF and glycolic acid (70%) can be mixed to yield SbFs and ammonium glycolate. No water is added but the water content of the glycolic acid and the water generated by the reaction are not removed. The

resulting mixture, which may be filtered, if necessary, before shipment, is a viscous liquid which presents to the plater no problem of dissolving solid material in his tank. The ammonium sulfate may not be necessary but if used should be shipped in solid form and added to the plating solution resulting from adding water to the concentrate. Or, the water to be added to the concentrate or a part thereof may be used to dissolve the ammonium sulfate and the resulting solution of ammonium sulfate, after being filtered if necessary, may be used for diluting the concentrate. In such a procedure, the final addition of NI'LlOH for adjusting pH is kept to a minimum. The pH before final adjustment will be about 2.5 to 3.0. This is very desirable because of the fumes resulting from adding ammonium hydroxide to the bath.

The following solutions (bath compositions) are suitable for shipment in steel drums, the attack on steel being negligible.

Molecular weights 1. SbzOs /2 NHiFHF 1 /2 Glycolic acid 1 /2 2. SbzOa /2 NHaFHF 1 /2 Glycolic acid 1 H2804 A Any mixture of these two solutions will possess the same lack of attack on steel.

A very excellent bath formulation, most of which can be shipped in the form of a concentrate, consists of (1) the product of mixing antimony trioxide, ammonium bifluoride, hydrogen fluoride and glycolic acid in the molar ratio indicated in Example 10 above, (2) 1.0 mol of ammonium sulfate, (3) water, (4) any desired addition agents and such quantity of ammonium hydroxide or hydrofluoric acid as may be necessary to adjust the pH to the desired point. The antimony trioxide, ammonium bifluoride, hydrogen fluoride and glycolic acid when mixed, form a clear, viscous solution which is satisfactory for shipping in concentrated form. The antimony trioxide, ammonium bifluoride, hydrogen fluoride and glycolic acid are in molecular ratio to react to form antimony trifluoride and ammonium glycolate, together with one mol of water for each mol of ammonium glycolate. The only water involved in making the concentrate is the water content of the (preferably glycolic acid and the water generated by the reaction. When the concentrateis to be made up into a plating solution, a satisfactory amount of water to be added is 2.7 parts by volume of water to 1 part of the concentrate. The ammonium sulfate is added to prevent immersion deposition and consequent poor adherence when the solution is used for the purpose of depositing antimony on a lead cathode. Sulfate ion is not necessary in all cases. It is not necessary when, for example, the deposit is made on copper. If sulfate is needed, a desirable concentration range is .81 to 243 grams per liter of sulfate ion.

Having thus described the invention, what is claimed 1. An aqueous antimony plating solution comprising antimony trifiuoride in concentration from 0.3 to 0.9 mol per liter, an aliphatic alpha hydroxy carboxylic acid in quantity from A2 to 2 alpha hydroxy equivalent weights per atomic weight of antimony and an alkaline compound in quantity to produce a pH between 2.5 and 5.0.

2. An aqueous antimony plating solution comprising antimony trifluoride in concentration from 0.3 to. 0.9 mol per liter, an aliphatic alpha hydroxy carboxylic acid of the class consisting of tartaric, citric, glycolic, gluconic, and lactic acids in quantity from A; to 2 alpha hydroxy equivalent weights per atomic weight of antimony and an alkaline compound in quantity to produce a pH between 2.5 and 5.0.

3. An aqueous antimony plating solution comprising antimony trifluoride in concentration from 0.3 to 0.9 mol per liter, ammonium glycolate in quantity from to 2 alpha hydroxy equivalent weights per atomic weight of antimony and an alkaline compound in quantity to produce a pH between 2.5 to 5.0.

4. An electroplating process comprising electrolyzing a solution according to claim 3 at a cathode current density within the range from to 200 amperes per square foot.

5. An aqueous antimony plating solution comprising antimony trioxide, ammonium bifluoride and glycolic acid in proportions from 0.3 to 0.9 mol of antimony trioxide per liter, 0.61 to 1.85 mols of ammonium bifluoride per liter and glycolic acid in quantity to prevent formation of a precipitate and within the limits from 0.61 to 1.85 mols per liter, and an alkaline compound in quantity to produce a pH between 2.5 to 5.0.

6. An electroplating process comprising electrolyzing a solution according to claim 5 at a cathode current density within the range from 10 to 200 amperes per square foot.

7. The invention as defined in claim 1 wherein further said solution contains from 81 to 243 grams per liter of sulfate ion.

8. The invention as defined in claim 3 wherein further said solution contains from 81 to 243 grams per liter of sulfate ion.

9. The invention as defined in claim 5 wherein further said solution contains from 81 to 243 grams per liter of sulfate ion.

10. An electroplating process comprising electrolyzing a solution according to claim 9 at a cathode current density within the range from 10 to 200 amperes per square foot.

11. As a new composition of matter, a plating concentrate, capable of use for electrodeposition of antimony upon addition of water thereto, said concentrate comprising the mixture resulting from the mixing of antimony trioxide, ammonium bifluoride and glycolic acid in approximately the proportions of 1% mol of NH4FHF and from 1 to 1 /2 mols of glycolic acid for each V2 mol of SbzOs, the same being a viscous solution suitable for electrodeposition of antimony upon dilution with 2.7 volumes of water per volume of said concentrate and adjustment of pH to from 2.5 to 5.0.

12. As a new composition of matter for use in electrodeposition of antimony, a solution comprising antimony trifluonde and ammonium glycolate in aqueous medium in approximately equimolecular proportions of SbFs and ammonium glycolate, antimony trifluoride being present in concentration from 0.3 to 0.9 mol per liter and the pH being in the range from 2.5 to 5.0.

Mathers et al.: Trans. Electrochemical Society, vol. 31 (1917), pp. 293-301.

Piontelli et al.: Chemical Abstracts, vol. 37 (1943), p. 1336. 

1. AN AQUEOUS ANTIMONY PLATING SOLUTION COMPRISING ANTIMONY TRIFLUORIDE IN CONCENTRATION FROM 0.3 TO 0.9 MOL PER LITER, AN ALIPHATIC ALPHA HYDROXY CARBOXYLIC ACID IN QUANTITY FROM 1/8 TO 2 ALPHA HYDROXY EQUIVALENT WEIGHTS PER ATOMIC WEIGHT OF ANTIMONY AND AN ALKALINE COMPOUND IN QUANTITY TO PRODUCE A PH BETWEEN 2.5 AND 5.0. 